Regulated power supply for mass spectrometers



Sept. 21, 1965 H. M. GRUBB ETAL REGULATED POWER SUPPLY FOR MASS SPECTROMETERS Filed OG'C. 2, 1963 4 Sheets-Sheet 1 @WUI/weeg Sept. 21, 1965 H, M. GRUBB ETAL. 3,207,894

REGULATED POWER SUPPLY FOR MASS SPECTROMETERS Filed oct. 2, 196s 4 sheets-sheet a llmhmllwllJ Sept. 2l, 1965 H. M. GRUBB ETAL REGULATED POWER SUPPLY FOR MASS SPEGTROMETERS Filed OCT.. 2, 1963 4 Sheets-Sheet 3 IN VEN TORS. /eawgf WZ f @Hoff/zeg QNN NWN wvl-.Illi- @WN ll VIII Sept- 21, 1965 H. M. GRUBB ETAL REGULATED POWER SUPPLY FOR MASS SPECTROMETERS Filed OC'b. 2. 1963 4 sheets-sheet 4 1N V EN TORS evmg 77]. am b 6fm/5% `H Jaa/'d M4# Q @mv/flag United States Patent O 3,207,394 REGULATED POWER SUPPLY FOR MASS SPECTRMETERS Henry M. Grubb and Charles H. Ehrhardt, Highland, Ind.,

assignors to Standard @il Company, Chicago, Ill., a

corporation of Indiana Filed Oct. 2, 1963, Ser. No. 315,115 1l) Claims. (Cl. Z50-JAS) This invention relates to an improved high voltage control system. More particularly, the invention concerns providing a high voltage control system for mass spectrometers and the like.

In many electrical devices it is essential to provide a high voltage D.C. of known value, and to vary this voltage in a controlled manner. Systems which have heretofore been available to accomplish this have generally been inordinately complex and have usually suffered the disadvantages of being inaccurate and non-linear.

This non-linearity is particularly important in mass spectrometers employed for analyzing compounds having masses in excess of a few hundred. As is well known, mass spectrometers usually deliver their output in the form of a photographic spectrogram, and markings of some sort are placed on the spectrogram to designate corresponding mass numbers. It is thus essential to relate mass number markings with the mass of the ion being collected, and this requires knowledge of the D.C. voltage applied to the spectrometer ion source. Even in those instances where the mass number markings correspond to actual mass numbers, the portion of the spectrogram between the markings is not in a linear relationship with mass numbers and it is still necessary to separately determine the D.C. voltage for a particular point between the markings and to calculate the mass number. Thus, unless the magnitude of this voltage is readily determinable it is extremely diicult to determine mass numbers corresponding to spectrograph peaks, particularly at high mass numbers.

A primary object of this invention is to provide a voltage control system suitable for employment with mass spectrometers which enables the spectrometer to deliver a continuous linear and accurate indication of mass numbers.

According to the invention we provide an electrical system including a reference voltage, to linearly vary the reciprocal of the D.C. high voltage with the position of a variable resistance in a parallel electrical circuit with the spectrometer, the position corresponding directly to an ion mass number. The variable resistance is changed from a first value to a second value and the change in the voltage in contrast to the reference voltage provides a signal to return the voltage of the variable resistance to the reference voltage which in turn changes the D.C. high voltage. The change in the DC. high voltage is such that its reciprocal varies in a linear relationship with the position of the variable resistance. This linear variation enables a direct reading of the ion mass number to be taken without a measurement of the D.C. high voltage and subsequent calculation of the mass number. The electrical system comprises a resistance means across the D.C. high voltage and in parallel with the mass spectrometer, the resistance means including a variable resistance, means for changing the value of the variable resistance across its range whereby a changing fraction of the D.C. high voltage is produced, means for producing a reference D.C. voltage, means for comparing the fractional D.C. high voltage with the reference D.C. voltage and producing an error A.C. voltage whose phase when the fractional voltage exceeds the reference voltage is different from that when the reference voltage exceeds the fracice tional voltage, means for converting the error A.C. voltage to an error D.C. voltage, and oscillator-rectier-ilter means for generating the D.C. high voltage whose output is controlled by the error D.C. voltage.

A major feature of the inventive system is that the position of the variable resistance is precisely linear with respect to the reciprocal of the high voltage D.C. output of the oscillator-rectier-tilter. As a consequence, by merely observing this variable resistance it is possible to determine at any given instant the precise mass number being scanned by a mass spectrometer. It is also within the ambit of our system to employ a motor to vary the resistance, and to change motor speed at preselected resistance positions so as to enable slow scanning at low mass numbers `and more rapid scanning at higher mass numbers, all the while preserving linearity.

Another important advantage stems from the linearity relationship between the position of the variable resistance and the inverse of the high voltage D.C. output. A mass marking system may be coupled to the variable resistance whereby an indication of mass number is recorded on the spectrometer record concurrent with the scanning of that mass. The mass scale so marked will be precisely linear.

Other objects and advantages of the inventive system will become apparent from the following description when read in conjunction with the attached drawings. In these drawings, numbers from l to 99 denote major elements and combinations depicted in the gures; numbers from 100 to 199 are reserved for resistors, numbers from 200 to 299 are capacitors, 30G-349 are vacuum tubes, 350- 399 are transformers, 400-449 are rectiers and crystal diodes, and 450-499 are switches and relays. In the drawings:

FIGURE l is an overall circuit diagram showing an embodiment of the invention as applied to a mass spectrometer ion source voltage control;

FIGURE 2 is a detailed circuit schematic of a high voltage control system;

FIGURE 3 is -a detailed schematic showing a mass spectrometer mass marker and scanning system for use in comunction with the circuit of FIGURE 2; and

FIGURE 4 is an isometric view of cams and gear wheels lemployed in lmoving the variable resistance and in effecting mass marking.

Turning rst to FIGURE 1, ion source 11 of a mass spectrometer is connected by line 12 to ionization-emission control chassis4 13, into which feeds high voltage D.C. E via line 14 from the inventive control system.

Connected into chassis in a manner detailed hereinafter is a conduit 19 which constitutes a portion of a feed back circuit for the high voltage control system. Conduit or resistance means 19 contains one or more fixed resistances designated as R0 and a variable resistance R. Conduit 19 thus samples voltage E applied from the high voltage control system and produces a fractional value of the D.C. high voltage.

n The variable center tap of resistance R is connected Via line 21 to high voltage chassis 16 which contains 4the electronic elements of the inventive high voltage control system.

In high voltage chassis 16 the sampled or fractional Voltage from conduit 21 is compared with a reference voltage obtained from a source of constant voltage 23 such as a battery or a Zener diode system. In the embodiment depicted in FIGURE l, such comparison is effected by employing as a means a synchronous modulator including armature 22 to convert the error signal resulting from a comparison of the sampled and the reference voltage into 60 cycle AC. whose phase when the sampled (or fractional) voltage exceeds the reference voltage is different from and normally opposite that when the reference voltage is greater. The alternating current is then amplified by amplifier 25, and thereafter rectified by armature 26a. For simplicity, synchronous rectifier of the vibrator type is shown in FIGURE l as the means for converting the A.C. voltage to D.C. voltage, although for improved results, particularly with respect to elimination of armature contact wear, a bridge type rectifier demodulator is substituted for the armature 26a.

The amplified and rectified error signal is filtered via resistances 26h and 26d and capacitor 26C and conducted via line 27 to serve as the grid bias of D C. amplifier 28. Here the error signal is further amplified and transmitted via conduit 29 to high voltage RF oscillator 32. Oscillator 32 is advantageously an electron tube push-pull selfexcited RF oscillator with resonant coils. The output of D.C. amplifier 28 determines the screen-grid voltage of high voltage RF oscillator 32 and hence the amplitude of its oscillations.

The high voltage RF output of oscillator 32 is conducted via line 33 to high voltage rectifier 34 and filter 36 whence it is converted to a filtered D.C. output E for transmission via line 14 to ionization emission control chassis 13.

With respect to line 31 and capacitor 221, these comprise a fast negative feedback loop from the high voltage output of high voltage chassis 16 to the input of D.C. amplifier 28.

Power for high voltage chassis 16 is obtained from D.C. power supply 15 and from 110 volt 60 cycle lines as shown.

Directing attention to mass marker chassis 18, this provides a means for continuously changing the position of the center tap of variable resistance R from a first value to a second value, and hence for continuously varying voltage E from high Voltage chassis 16. Such means may comprise a synchronous electric motor 41 adapted by suitable linkwork mechanism to drive the center tap of variable resistance R. Power for motor 41 is derived from lines 42 which are connected to an arrangement of rectifier 46, lter 47, positive grid bias multivibrator, and power amplifier 49. This latter system produces a plurality of fixed-frequency A.C. outputs to power motor 41 at a speed proportional to the selected frequency. By changing the positive grid bias applied to multivibrator 48 this frequency can be varied at will. It is preferred to change the oscillation frequency, and hence motor 41s speed, by connecting the positive grid bias input via a multiposition switch 44 which changes the value of this positive grid bias at preselected positions of variable resistance R. Details of a mechanism for accomplishing this are reserved for a discussion of FIGURE 4.

In operation, variable resistance R may be, for example, a 15 turn Helipot driven by motor 41 and suitable linkwork mechanism, also lreserved for FIGURE 4. With the feedback of line 19 in proper operation, the voltage of line 21 will be almost exactly the same as the voltage produced by constant potential source 23. Hence the high voltage D.C. output at E (line 14) is indirectly controlled to give the proper voltage across the tap or slider on variable resistance R. In other words, as motor 41 positions the slider on variable resistance R, D C. output voltage E is readjusted to maintain a constant voltage at line 21 having a magnitude substantially equal to that produced from constant potential source 23. Consequently, the high voltage D C. output of E will be related to the position of the variable tap on variable resistance R.

This relationship, according to the device of the present invention, is precisely inversely linear. This may be demonstrated by the following mathematical analysis which demonstrates that the mass of ions is linear and the high voltage output is inversely linear with respect to the position of the tap on variable resistance R.

4 j The standard equation relating to the parameters determining the mass number of ions focused on the exit slit of a mass spectrometer is 1 er2II2 1 m- -w --(eonstant) where m is the mass being focused, E is the accelerating potential, e is the electronic charge, r is the radius of the ion path, and H is the magnetic field intensity. Thus during scanning, m will be inversely proportional to E at a constant magnetic field strength.

The voltage at the variable tap of variable resistance R is ER E HP RT where R is the resistance between the tap and ground and RT is the total resistance between the high voltage terminal and ground (including all resistances in the ionization emission control chassis, resistance Rd, and resistance R). Since BHP is maintained closely equal to Estd from constant potential source 23 by the high voltage chassis 16 circuit 1 :R (constant) RT EEP (RTEstd) Thus if dR/ dt is constant, dm/ dt is also constant.

This relationship permits two additional advantages to be attained. First, it is usually necessary to use at least two different magnetic field values in order to scan the desired mass range. 'I'he constant on the right side of the equation above changes with H2. It is evident that the quantity by which R is multipled can be maintained constant at different magnetic field values by keeping the ratio of HZ/Estd constant when the magnetic field is changed. In the preferred embodiment of the instant invention, this is accomplished by adjusting Estd from constant potential source 23 to match the value of H, or in other words to adjust the reference potential when magnetic field strength is changed.

It will be appreciated that the above advantage enables scanning rate to remain unchanged irrespective of magnetic field strength; the mass number is always equal to the product of R by a combined constant which is independent of the magnetic field. Thus, the aforementioned advantages are (l) when the magnetic field is changed an appropriate value of Estd is obtained by a simple selector switch, and the controlling variable resistance R need not be reset and (2) since the mass num ber is always proportional to R, the dial of variable resistance R may be made to read directly in mass number. This latter advantage is embodied in FIGURE 4 and will be discussed in conjunction with `that figure.

Turning now to FIGURE 2, a detailed schematic diagram of the high voltage chassis 16 is depicted. Reference numerals in FIGURE 2 conform exactly with the identical components of FIGURE l.

The input to the system is designated by a circle A and is transmitted via line 21 to commercial chopper 22 for comparison with a reference voltage from constant potential source 23.

Constant, potential source 23 may comprise a standard cell or, in the embodiment depicted in FIGURE 2, a Zener diode 401. The several resistances shown in the dotted box constant potential source 23 are for the purpose of permitting source 23 to be adjustable and deliver two different Estds. This is for the purpose of maintaining the mass number always equal to the position -of variable resistance R times a single constant irrespective of the magnetic field strength in the mass spectrometer, as described above.

Thus both the sampled voltage from variable resistance R and the reference voltage Estd are fed into chopper 22, which delivers a 60 cycle error signal to 60 cycle amplifier 25. This error signal will be null when` the reference m (constant) potential and the sampled voltage from variable resistance R are exactly equal.

Sixty cycle A.C. amplifier 25 is advantageously a double triode amplifier of the type which may be obtained commercially from such suppliers as Brown Instrument Company. Amplifier 25 amplilies the error signal by about 10,000 times and delivers it Via capacitor 208 to synchronous rectifier 26. Synchronous rectifier 26 was shown-in FIGURE 1 as constituting an armature 26a for the sake of simplicity. In actuality, it has been found that a bridge type rectifier demodulator is more preferable since it avoids contact wear. Bridge type rectifier demodulators having transformers such as transformer 354 with a split primary in series and a pair of secondary windings in parallel, connected with rectiiers 402, 403, 404 and 405 are well known and need not be described further.

The output for synchronous rectifier 26 is a fluctuating D.C., and is conducted via line 27 through a filter comprising resistances 126, 127, 128 and capacitors 209, 210, and 211 to D.C. amplifier 28, where it is applied as a grid bias to tube 306. Tube 307 is a screen voltage control tube. A cathode follower comprising tube 305 is included as a component of D.C. amplifier 28.

The output of lamplifier 28 is transmitted via line 29 to high voltage RF oscillator 32. Oscillator 32 is advantageously a push-pull oscillator employing vacuum tubes 301 and 302 with inductive coupling via air core transformers 350 and 351. Line 29 controls the screen voltage of tubes 301 and 302 and thereby affects the gen# eration of an oscillatory RF current having a voltage amplitude increasing with the magnitude of the input voltage to oscillator 32 (line 29).

The output from oscillator 32 is taken at lines 33, rectified by high voltage rectifier 34-a full wave output rectifier including tubes 303 and 304-and filtered in high voltage filter 36.

The output at line 14-31 constitutes the high voltage D.C. output E of the system, and line 14 conducts this to the ionization emission control chassis 13 (of FIGURE l) while line 31 conducts it via capacitor 221 to serve as a fast negative feedback to the input of D C. amplifier 28.

Inviting attention to FIGURE 3, a detailed schematic is shown which corresponds to mass marker chassis 18 and resistance R0 of FIGURE 1. In the dotted box at the upper part of FIGURE 3 is shown a group of resistances, of which resistances 140, 141, 142 and 143 are embodied in a commercial ionization emission control chassis 13 of the type manufactured by Consolidated Electrodynamics. Other arrangements of resistances may be provided by those skilled in the art to accommodate the voltage control system of the present invention.

It will be seen in FIGURE 3 that line 21 connects with the slider or variable tap of Variable resistance R (also designated as resistor 108). The position of this slider is controlled by the symbolic dotted line passing through motor 41 and representing a suitable linkwork.

Motor 41 is a synchronous motor which, in the embodiment depicted, is fed with current via line 42. Its power is 30 cycles at 55 volts in the S position of switch 44; 60 cycles at 110 volts in the M position, and 120 cycles at 180-200 volts in the F position. Scanning is conducted at a slow rate (S position) when the mass is below 100, at a medium rate (M position) when the mass is between 100 and 300, and at a fast rate (F position) at masses above 300; it will be appreciated that these changeover points may be preselected at any desired mass number.

Power for motor 41 is derived from power amplifier 49, positive grid bias multivibrator 48, and a voltage rnultiplier which is shown in the left hand portion of FIG- URE 3. The frequency at which positive grid bias multivibrator 48 operates is determined by the positioning of variables resistances 146, 1477 and 148. By selecting the particular voltage applic-d to the control grid of tube 310, positive grid bias multivibrator 48 is caused to oscillate at any of three preselected frequencies. The output yof positive grid bias multivibrator 48 is conducted via resistances 155 and 156 to a power amplifier `stage 49 comprising twin triode tube 311, the output of which is matched to the impedance of motor 41.

Switch 453 is mechanically linked to motor 41 and changes the frequency applied to this motor from 30 cycles to 60 cycles when tripped. Similarly, switch 454 changes frequency from 60 cycles to 120 cycles. Switches 453 and 454 operate through relays 458, 459, and 460.

Switch 455 operates through relay 457 to cause mass marker lamp 51 to light at each 100 mass numbers, and switch 456 and relay 458 cause mass marker lamp 51 to light once at every l0 mass numbers. Switches 455 and 456 are tripped by lobes of cams 505 and 506 which are connected to motor 41.

The means by which motor 41 changes the variable tap of variable resistance R and at the same time effects mass marking and preselected scanning rate changes are shown in FIGURE 4, and attention is directed to that figure.

Motor 41 drives shaft 511 and 24tooth gear 512, which in turn drives 60tooth gear 513 and shaft 515. A clutch 514 engages gear 513 with shaft 515 upon application of spring pressure from spring 516 and toggle 517. Shaft 515 also drives 56-tootl1 gear 518 and a 5-lobe cam 506. The lobes on cam 506 activates switch 456 so as to cause flashing of mass marker lamp 51 (FIGURE 3) at every l0 mass units.

Gear 518 meshes with 59-tooth gear 522 on shaft 523. An arrangement of wedged block 521 on gear 522 and pinion 519 on gear 518 causes these gears to lock in eX- treme positions so as to avoid exceeding the limits of variable resistance R.

Gear 522 in turn meshes with 1l2-tooth gear 524 on shaft 526. A mass indicator dial 532, graduated in peripheral units, visibly indicates the mass being scanned. Single lobe cam 505, likewise on shaft 526, trips switch 455 to cause a second flashing of mass marker lamp 51 (FIGURE 3) when every 100 mass units is reached.

It will be appreciated that mass marker lamp 51 is employed in conjunction with a photographic mass spectrometer record. It is within the scope and spirit of the present invention to employ alternative marking systems, such as inked lines, punches in paper, signals on magnetic tape or wire, or the like.

Shaft 526 also accommodates 48-tooth gear 527 which connects with 24-tooth gear 528 on shaft 529 which drives the variable tap on lS-turn Helipot which constitutes variable resistance R.

Also mounted on shaft 526 is 16-tooth gear 531 which meshes with 1Z0-tooth gear 533 on shaft 534. Shaft 534 mounts cams 504 and 503 having lobes which register with switches 454 :and 453 respectively. Switch 453 changes the frequency applied to motor 41 via lines 42 from 30 cycles to 60 cycles at mass 100, and switch 454 changes the frequency from 60 cycles to 120 cycles at mass 300.

In operation, motor 41 rotates at, say one-half revolution per minute when fed with 30 cycles current. It continues rotation at this speed beginning with, say, mass 25 until mass 100 is reached. At masses 30, 40, 50, 60, 70, 80, 90, and 100, cam 506 trips switch 456 to cause mass marker lamp (FIGURE 3) to mark the spectrometer record. At mass 100 a second mark is established when the lobe on cam 505 trips switch 455.

Switch 455 also accomplishes another purpose. When a mass of about 93 is reached switch 453 is tripped and completes a series of connections involving a relay governed by switch 455. By this arrangement, switch 453 serves to change the frequency applied to motor 41 from 30 cycles to 60 cycles at precisely the time when switch 455 signals that mass 100 has been reached.

From mass 100 up until mass 300 scanning is performed at double the rate at which sub-100 masses were scanned. At a mass of about 92, according to conventional procedures, the magnetic iield strength of the mass spectrometer is manually changed; at the same time the switch in constant potential source 23 (FIGURE 2) is placed in its alternative position so as to enable scanning and mass marking to continue in a manner which remains linear with respect to the position of variable resistance R.

From mass 100 to mass 300 the record is again marked with one mark for every mass numbers and a double mark at 200 and 300 mass numbers.

At a mass of about 293 switch 454 is tripped by cam 504, and when the mass reaches 300 switch 455 causes (1) a second mass mark to appear on the spectrometer record and (2) switches the frequency applied to synchronous motor 41 from 60 cycles to 120 cycles. Scanning is continued beyond mass 300 at the now-doubled scanning rate for as long as desired.

Thus We have provided a high voltage control system which is particularly useful for mass spectrometry work since it permits complete inverse linearity between the high voltage output and one or more elements in the circuit, specically variable resistance R. In actual test the inventive device has been found unusually free from noise, and adaptable to changes in scanning rates at any of a variety of preselected mass numbers. Calibration has been found to be exceptionally simple, and is effected merely by setting the position of variable resistance R to conform with a selected peak from a known compound, and adjusting resistances 167 and 169 (FIGURE 2) rst for high mass (resistance 167) and then for low mass (resistance 169) readings. Because of its rapid convergence, calibration is exceedingly rapid.

Selected values of resistors, capacitors, vacuum tubes, transformers, rectiers and crystal diodes, switches and relays, and inductances which were actually employed in a device constructed according to the foregoing principles are set forth below.

Resistors: Ohms Resistors: Ohms 101 100K 137 200 102 138 96,088 103 3500 139 100K 104 9.5K 140 100K 105 10K 141 3.615M 106 1K 142 100K 107 150K 143 100K 108 50K 144 100 109 100K 145 50 110 1M 146 80 mfd. 111 150K 147 100K 112 1M 148 100K 113 1M 149 82K 114 2.2M 150 47K 115 1M 151 47K 116 50K 152 47K 117 1M 153 1M 118 15K 154 1M 119 2.7M 155 47K 120 2.7K 156 47K 121 15K 157 500K 122 75K 158 500K 123 75K 159 25K, 5 w 124 75K 160 25K, 5 w 125 75K 161 150K 126 100K 162 47K 127 100K 163 1000 131 700K 167 200 132 2M 168 5K 8 Capacitors, in microfarads, unless otherwise indicated:

201 0.04 217 2x0.1 202 0.05 218 var. 203 +10 219 500 204 .02 220 500 205 +10 221 1000 206 .05 222 0.05 207 .02 223 50 208 8 224 50 209 0.25 225 210 0.25 226 .0088 211 0.25 227 .0088 212 0.1 228 .05 213 0.1 229 .05 214 0.003 230 8 215 0.1 231 20 216- -501 232 20 Vacuum tubes:

301 5881 307 OA2 302 5881 308 12Ax7 303 3A3 309 12Ax7 304 3A3 310 12BH7 305 12BH7 311 6AS7 306 6AU6 Transformers 350 Miller 4526. 351 Miller 4526. 352 Stancor P-8l90. 353 UTC A-19. 354 UTC A-26.

Rectiers and crystal diodes:

401 IN430. 402 Hughes HD 6751. 403 Hughes HD 6751. 404 Hughes HD 6751. 405 Hughes HD 6751.

Switches and relays:

457 KCP 11 458 KCP 14 459 KCP 14 460 KCP 14 Inductances:

501 30 mh, 100 ma 502 30 mh, 100 ma Obviously many alternatives, modifications, and variations will be apparent to those skilled in the art in view of the foregoing description. Thus, a Wien bridge oscillator may be employed in lieu of positive grid bias multivibrator 48. Also transistor components may be substituted in whole or in part for the vacuum tubes shown, and in this connection attention is invited to A Handbook of Selected Semiconductor Circuits, Navships 93484, NObsr 73231, prepared for the Bureau of Ships,1

Department of the Navy. It is intended to embrace these and other alternatives, modifications, and variations as fall within the spirit and broad scope of the invention, as well as to embrace all other uses for the inventive high voltage control circuit as fall within the scope of the appended claims.

This is a continuation-impart of copending application S.N. 46,466, led August 1, 1960, now abandoned.

We claim:

1. In a mass spectrometer supplied with an ion source and a source of D.C. high voltage, an electrical system including a reference voltage, to linearly vary the reciprocal ofthe D.C. high voltage with the position of a variable resistance in a parallel electrical circuit with said spectrometer, said position corresponding to an ion mass number, said linear variation enabling a direct reading of the ion mass number to be taken Without a measurement of said D.C. high voltage and subsequent calculation of a mass number, said electrical system comprising:

(a) a resistance means across said D.C. high voltage and in parallel with said mass spectrometer, said resistance means including a variable resistance,

(b) means for changing the value of said Variable resistance from a first value to a second Value whereby a changing fraction of the D.C. high voltage is produced,

(c) means for producing a reference D.C. voltage,

(d) means for comparing said fraction of said D.C. high voltage with said reference D.C. voltage and for producing an error A.C. Voltage whose phase when said fractional D.C. voltage exceeds said reference D C. voltage is diterent from that when said reference D.C. voltage exceeds said fractional D.C. voltage,

(e) means for converting said error A.C. voltage to an error D.C. voltage, and

(f) oscillator-rectier-filter means for generating said D C. high voltage whose output is controlled by said error D.C. voltage.

2. The system of claim 1 wherein said oscillator-rectier-lter means includes a Vacuum tube push-pull oscillator.

3. The system of claim 1 wherein said means for producing said error A.C. voltage from said comparison 'of the D.C. voltages includes a synchronous vibrator.

4. The system of claim 1 wherein said means for converting said error A.C. voltage to said error D.C. voltage includes a bridge type rectier demodulator.

5. The system of claim 1 wherein said means for producing a reference D.C. voltage includes a Zener diode.

6. The system of claim 1 wherein said means for producing said error A.C. voltage includes an A.C. amplifier.

7. The system of claim 1 including means for changing said variable resistance at a constant rate.

8. The system of claim 7 including means for changing the rate at preselected positions of said variable resistance.

9. The system of claim 7 wherein said means for changing said variable resistance includes a synchronous motor receiving power from a positive grid bias multivibrator.

10. In a mass spectrometer supplied with an ion source and a source of D.C. voltage, and provided with means for making mass number markings on the record of said mass spectrometer, the electrical system of claim 7 including a means for driving said mass marking means at a rate proportional t0 the rate of change of said variable resistance.

References Cited by the Examiner UNITED STATES PATENTS 2,575,711 11/51 Hipple et al Z50-41.9 2,728,858 12/55 Ziffer 321-2 2,792,542 5/ 57 Robinson Z50-41.9 2,798,957 7/57 Holden et al. Z50-51.5 2,815,479 12/57 Rechnitzer Z50-41.9 2,837,655 6/58 Lang Z50-51.5

RALPH G. NILSON, Primary Examiner. 

1. IN A MASS SPECTROMETER SUPPLIED WITH AWN ION SOURCE AND A SOURCE D.C. HIGH VOLTAGE, AN ELECTRICAL SYSTEM INCLUDING A REFERENCE VOLTAGE, TO LINEARLY VARY THE RECIPROCAL OF THE D.C. HIGH VOLTAGE WITH THE POSITION OF A VARIABLE RESISTANCE IN A PARALLEL ELECTRICAL CIRCUIT WITH SAID SPECTROMETER, SAID POSITION CORRESPONDING TO AN ION MASS NUMBER, SAID LINER VARIATION ENABLING A DIRECT READING OF THE ION MASS NUMBER TO BE TAKEN WITHOUT A MEASUREMENT OF SAID D.C. HIGH VOLTAGE AND SUBSEQUENT CALCULATION OF A MASS NUMBER, SAID ELECTRICAL SYSTEM COMPRISING: (A) A RESISTANCE MEANS ACROSS SAID D.C. HIGH VOLTAGE AND IN PARALLEL WITH SAID MASS SPECTROMETER, SAID RESISTANCE FROM A FIRST VALUE TO A SECOND VALUE WHEREBY (B) MEANS FOR CHANGING THE VALUE OF SAID VARIABLE RESISTANCE FROM A FIRST VALUE TO A SECOND VALUE WHEREBY A CHANGING FRACTION OF THE D.C. HIGH VOLTAGE IS PRODUCED, (C) MEANS FOR PRODUCING A REFERENCE D.C. VOLTAGES, (D) MEANS FOR COMPARIING SAID FRACTION OF SAID D.C. HIGH VOLTAGE WITH SAID REFERENCE D.C. VOLTAGE AND FRO PRODUCING AN ERROR A.C. VOLTAGE WHOSE PHASE WHEN SAID FRACTIONAL D.C. VOLTAGE EXCEEDS SAID REFERENCE D.C. VOLTAGE IS DIFFERENT FROM THAT WHEN SAID REFERENCE D.C. VOLTAGE EXCEEDS SAID FRACTIONAL D.C. VOLTAGE, (E) MEANS FOR CONVERTING SAID ERROR A.C. VOLTAGE TO AN ERROR D.C. VOLTAGER, AND (F) OSCILLATOR-RECTIFIER-FILTER MEANS FOR GENERATING SAID D.C. HIGH VOLTAGE WHOSE OUTPUT IS CONTROLLED BY SAID ERROR D.C. VOLTAGE. 